Genes may help predict infidelity

Genes may help predict infidelity, study reports

Nov. 30, 2006
Special to World Science

The chance that in­fi­del­i­ty will in­trude on a ro­man­tic re­la­tion­ship may be part­ly writ­ten in the cou­ple’s genes, a stu­dy has found.   The re­sults sug­gest a DNA test could tell a man the rough chances his fe­male part­ner will cheat on him, though it would­n’t nec­es­sar­i­ly work the op­po­site way.

The study found that wom­en act less pas­sion­ate­ly toward — and are like­li­er to cuck­old — part­ners who share genes with them in a spe­cial part of the ge­nome.   This may in part re­flect an ev­o­lu­tion­ary mech­a­n­ism to re­duce in­breed­ing, the in­ves­ti­ga­tors spec­u­lat­ed.

In­fi­del­i­ty touches about half of all coup­les, mar­ried or not, ac­cord­ing to Not Just Friends, a 2002 book by psy­chi­a­trist and in­fi­del­i­ty re­search­er Shir­ley Glass.   And last year, sci­ent­ists re­ported that one in 25 dads may be rais­ing ano­ther man’s child.

In the new stu­dy, re­search­ers with the Uni­ver­si­ty of New Mex­i­co, Al­bu­quer­que, fo­cused on a set of genes that past stud­ies have im­p­li­cat­ed in a link be­tween sex­u­al at­trac­tion and ge­net­ic sim­i­la­ri­ty.

The clus­ter of genes is termed the ma­jor his­to­com­pat­i­bi­li­ty com­plex, or MHC.   The genes, on hu­man Chro­mo­some 6, are in­volved in im­mune re­sponses.   The study is the first “to test the hy­poth­e­sis that MHC sim­i­larity pre­dicts as­pects of ac­tu­al hu­man sex­u­al re­la­tion­ships,” the re­search­ers wrote.   The find­ings ap­peared in the Oc­to­ber is­sue of the re­search jour­nal Psy­cho­log­i­cal Sci­ence.

MHC genes pro­duce mo­le­cules that en­a­ble cells to rec­og­nize in­tru­sive par­a­sites.    The mo­le­cules and the genes are ex­treme­ly di­verse and fast-evolv­ing.    Bi­ol­o­gists think these traits may be ev­o­lu­tion­ary mech­an­isms to help or­gan­isms stay a step ahead in the arms race with par­a­sites.

This may al­so ex­plain past stud­ies sug­gesting that hu­mans and an­i­mals pre­fer mates with dissi­m­i­lar MHC genes, ac­cord­ing to some sci­en­tists. Such a pre­ference might help as­sure that off­spring have a wide range of im­mu­ni­ty genes in the hol­ster, giv­ing them an edge over pa­th­o­gens.

Studies have even point­ed to a pos­si­ble route by which peo­ple sub­con­scious­ly as­sess potential mates’ MHC com­pat­i­bil­ity:  smell. In the mid-1990s, re­search­ers found that peo­ple sniff­ing T-shirts worn by oth­ers tended to pre­fer the odor of those whose wear­ers were least like them in this ge­netic re­gion.

Sev­er­al years lat­er, sci­en­tists linked si­m­i­lar pre­ferences to sex­u­al fi­del­i­ty in birds.     Il­le­git­i­mate chicks in three spe­cies of typ­i­cal­ly mo­nog­a­mous shore­birds showed up most­ly in the nests of gen­ti­cally si­m­i­lar par­ents, in­ves­ti­ga­tors found—al­though it was­n’t clear wheth­er the ma­jor his­to­com­pat­i­bi­li­ty genes spe­ci­fi­cal­ly played a role.    The study ap­peared in the Oct. 10, 2002 is­sue of the re­search jour­nal Na­ture.

The new study ech­oes el­e­ments of both pre­vi­ous stud­ies.

The researchers stud­ied 48 male-fe­male cou­ples who were ei­ther dat­ing “ex­clu­sive­ly,” by their de­scrip­tion, or mar­ried or liv­ing to­geth­er.

As the pro­por­tion of MHC genes the cou­ple shared in­creased, “wom­en’s sex­u­al re­spon­siv­ity to their part­ners de­creased, their num­ber of [out­side] sex­u­al part­ners in­creased, and their at­trac­tion to men oth­er than their pri­ma­ry part­ners in­creased,” the re­search­ers wrote in a pa­per de­scrib­ing their find­ings.

Two quantities were almost equal on av­er­age, ac­cord­ing to Chris­tine Garver-Apgar, the study’s lead au­thor:  the frac­tion of MHC genes shared, and the wo­man’s num­ber of extra part­ners.    In oth­er words, if the man and woman had half the genes in com­mon, the woman would have on av­er­age near­ly half a lov­er on the side.

But these ten­den­cies were found on­ly for wom­en; men’s at­trac­tion and like­li­hood of cheat­ing ap­peared un­re­lat­ed to the genes, the re­search­ers wrote.   Nor did these mol­ecu­lar sta­tis­tics seem to af­fect other aspects of re­la­tion­ships.   “MHC shar­ing,” the sci­ent­ists wrote, “does not broad­ly pre­dict re­la­tion­ship sa­tis­fac­tion.”

Don't think we can test for these . . . . . . . . . . . . yet.

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